This invention relates to a valve disabling device for use in an internal combustion engine, and more particularly to control means for such valve disabling device.
High output type internal combustion engines include a type equipped with a plurality of inlet valves and/or exhaust valves at each of the cylinders (hereinafter called "the multi-valve engine"). In the multi-valve engine, the communication passageway between the intake passage and/or the exhaust passage and the combustion chamber in each of the cylinders, which is alternately closed and opened by the inlet valves and/or the exhaust valves (hereinafter merely called "the valves" unless otherwise specified), has a relatively large total effective area of section so as to permit large quantities of a mixture and/or exhaust gases to be supplied into and/or emitted from the engine cylinder, thereby achieving high speed and high output operation of the engine.
However, the multi-valve engine suffers from a degradation in the engine output during operation in a low speed region. This is due to reduced charging efficiency which is caused by sucking of a reduced quantity of intake air into the combustion chamber through the above communication passageway having a large total effective area of section during engine operation in such low speed region, or caused by direct passing of intake air from the intake port to the exhaust port, which generally takes place during engine operation in such low speed region, and more frequently in the multi-valve engine in which the total sectional area of the inlet port or the exhaust port is large. In other words, while in internal combustion engines in general, the suction of a mixture into an engine cylinder is effected due to the inertia of intake air as well as a vacuum developed in the engine cylinder during the suction stroke, the inertia of intake air is small and direct passing of intake air from the inlet port to the exhaust port takes place while the engine is operating in a low speed region, resulting in a degradation in the engine output.
To overcome such disadvantages, it has generally be employed to disable or render inoperative part of the inlet valves and/or the exhaust valves during engine operation in a low speed region to keep same in a closed position, or to design the communication passageway between the intake passage and/or the exhaust passageway and the combustion chamber to be small in sectional area so as to obtain sufficient inertia of intake air or reduce the possibility or rate of direct passing of intake air from the inlet port to the exhaust port even during engine operation in a low speed region.
A curve of the rotational speed-output characteristic of the multi-valve engine obtained when part of the valves are rendered inoperative crosses with a curve of the same characteristic obtained when all the valves are operative, at a particular rotational speed N1 of the engine. The former is superior to the latter in an engine speed region lower than the speed N1, whereas the latter is superior to the former in an engine speed region higher than the particular speed N1. This rotational speed N1 remains nearly constant even with a change in the valve opening .theta.th of a throttle valve in the intake passage. This fact implies that if the engine is operated with part of the valves inoperative when the engine rotational speed Ne is lower than the speed N1, whereas the engine is operated with all the valves operative when the engine rotational speed Ne is higher than the particular speed N1, as employed by a conventional valve disabling device of this kind, a drop in the engine output can be avoided during engine operation in a low speed region even in the multi-valve engine.
On the other hand, in the event that an engine is operated in a non-loaded condition, for instance, if an engine installed in a vehicle is operated with the clutch in a disengaged state or the transmission in a neutral position whereby no power tranmission takes place from the engine output shaft to the driving wheels, no higher engine output is required than one sufficient to permit racing of the engine or mere operation of the throttle valve through an accelerator, to achieve satisfactory engine performance.
In such a non-loaded condition of the engine, it suffices to operate the engine with part of the valves inoperative to maintain stable operation of the engine, even in a high speed region. Further, the engine speed can increase within a very short rise time in response to changeover of the valve disabling device from a state wherein part of the valves are inoperative (hereinafter called "the partial valve inoperative state") to a state wherein all the valves are operative (hereinafter called "the all valve operative state"), during racing of the engine such that the engine rotational speed Ne at which the changeover is actually effected is higher than the particular speed N1 by certain rpm .alpha., even if the valve disabling device is adapted to effect such changeover at the particular engine speed N1, causing a sudden increase in the engine output, which in turn leads to a large mechanical shock applied to engine component parts as well as to the valve disabling device.
Moreover, as the throttle valve opening .theta.th decreases, the absolute quantity of intake air decreases due to the throttling action of the throttle valve. It has been found that as a consequence of this, when the throttle valve opening .theta.th is less than a predetermined value equal, e.g. to 1/16 times as large as the maximum valve opening, a superior engine output characteristic is obtained in the partial valve inoperative state to one obtained in the all valve operative state, throughout the whole engine speed region. Particularly, in an engine for vehicles, the capability of maintaining the operation of the engine with a high gear ratio of the transmission (TOP SLOW) at the lowest possible rotational speed is a barometer for the driveability of the vehicle and the operational flexibility of the engine. To this end, it is important that the engine should exhibit a satisfactory output characteristic when the throttle valve opening .theta.th is reduced to a very small value. Therefore, it is desirable to operate the engine in the partial valve inoperative state when the throttle valve assumes a small valve opening, and in a low engine speed region in particular.
In addition, if the valve disabling device for effecting changeover between the all valve operative state and the partial valve inoperative state is formed by an oil hydraulic means which is incorporated in the engine oil circulation system of the engine to utilize engine oil as operating fluid, when the engine oil is low in temperature and accordingly high in viscosity, the engine oil within the valve disabling device has reduced fluidity, which can degrade the responsiveness of the valve disabling device. As a consequence, assuming that the aforementioned particular rotational speed N1 is set at 2,000 rpm for instance, the changeover from the partial valve inoperative state to the all valve operative state will actually be effected at an engine rotational speed of 2,000 rpm plus rpm .beta., the rpm corresponding to an increase in the viscosity of the engine oil. If an engine equipped with such valve disabling device is installed in a vehicle, there can occur a sudden change in the engine output at the time of changeover operation of the valve disabling device, creating an unpleasant feeling to the driver or passengers.